Recently, in line with miniaturization, lightweight, thin profile, and portable trends in electronic devices according to the development of information and telecommunications industry, the need for high energy density batteries used as power sources of such electronic devices has increased. Currently, research into lithium secondary batteries, as batteries that may best satisfy the above need, has actively conducted.
Various types of carbon-based materials including artificial graphite, natural graphite, or hard carbon, which may intercalate/deintercalate lithium ions, have been used as an anode active material of a lithium secondary battery. Graphite among the above carbon-based materials has been most widely used, because it may provide advantages in terms of energy density of the lithium battery and may secure long lifetime of the lithium secondary battery due to its excellent reversibility.
However, since the graphite may have low capacity in terms of energy density per unit volume of an electrode and may facilitate a side reaction with an organic electrolyte solution at a high discharge voltage, there may be a risk of fire or explosion due to the malfunction and overcharging of the battery.
Therefore, a metal-based anode active material, such as silicon (Si), has been studied. It is known that a Si metal-based anode active material exhibits a high lithium capacity of about 4,200 mAh/g. However, a volume change of a maximum of 300% or more may occur before and after the reaction with lithium, i.e., during charge and discharge. As a result, there is a phenomenon in which the performance of the battery may degrade because a conductive network in the electrode may be damaged and contact resistance between particles may increase.
Thus, a method has been attempted, in which substantial changes in a diameter according to the volume change are reduced by decreasing the size of the silicon particles from a typical micron size to nanoscale. However, there may be many difficulties in a method of synthesizing a uniform nano silicon anode active material and uniformly distributing the nano silicon anode active material in a slurry.
In order to address such difficulties, nanowires, in addition to carbon nanotubes, have received attention as a nanomaterial that is the closest to commercialization as high-performance nanodevices, such as field effect transistors, photodetectors, chemical sensors and biosensors, nanoscale lasers, and light-emitting diodes (LEDs) using one-dimensional nanowires, begin to be realized.
As examples of such techniques, a method of forming nanowires by injecting silicon in a gas state and applying high heat or a method of growing nanowires by directly heating a silicon wafer has been developed. However, in these cases, the performance of the battery may degrade due to the detachment and weak electrical contact of the silicon nanowires during the preparation of the slurry or the operation of the battery.
Therefore, there is an urgent need to develop an anode active material for addressing the above limitations.